Dissolving cillulose



Patented Aprt"22, '1947" I v n x410341 7 meantimesum x. a.

' No nr'mnranumusimwraim.

' This invention relates to the method of Itrelates, parsolutions ofoellulosic material.

ticularly; to dissolving cellulose inaqueoussolutions of an alkali metalzincate or:hvdroxide.

The application ls a continuation in parts! my copending application.Ber.- No'. 483,!1'3': filed I or it. solution'with the cellulose,thesame en- April 20, 1943,1by me and entitledlsolubilized cellulose andmethod oi-makingwhichhag now been issued as Patent 2,357,731, which-inturn contains subject matter derived from my, application Serial No.407,445 filed August 19, 1941,

which has now beenissued as Patent 2,322,427.

This copending application describes, the dis solving of the celluloseln-sodium zincate solution under special conditions. g I

I have now discovered that when cellulose fiber of a certain maximumlength is used, the dissolving. of cellulose in zincate is promoted, theI cellulose is soluble in sodium hydroxide solutions under a wider rangeof conditions thanv otherwise, and the resulting solutions are free fromeral conditionsare used for eiiecting the solution.

The hydroxide solution is used suitably at an initiaigooncentration ofabout 15 to parts and preferably 16 to 30 parts of sodium hydroxide forparts of water. When the sodium hydroxide used initially is not to bediluted substantially, the concentration used should be about 8 to 12and preferably 8 to 10 parts of the alkali for 100 parts oi water. Theuse of such a solution without dilution requires a low temperature todissolvethe cellulose, say temperatures from plus 5 to 0" 0. down tothetemperature at which an. inorganic component of the solution begins tovcrystallize, as by freezing of water present. In

case there is used initially the relatively strong solution of sodiumhydroxide followed by dilution, theproportion of water used in effectingthe dilution is such as to lower the concentration in the final solutionto 6 to 12 and preferably 8 to 10 parts of sodium hydroxide for 100parts of objectionable quick gellingwhich is characteristic of thosemade under otherwise comparable conditions from fibers of longer length.

-The invention comprises the method of and the product resulting fromtreating cellulose fibers of mean length not substantially above 200 1microns and preferably of mean length ,not above 140 micronstwith asolution of anfalkalimetal hydroxide or an alkali metal zincatecontaining ,productiou oiupractica'lly clear, stable solutions.

an excess of alkali metal hydroxide, the :eolution,

of the short fiber cellulose being effected either by cooling thecellulose in contact with the h!!- droxide or zincatesolution to allowtemperature; say of 0 to 10C., or by contacting the cellu-,

lose with a relatively concentrated. SOIUtlOll-uOf the hydroxide orzincate and then diluting with water at temperatures that may beconsiderably above the said low temperature. 7

Unless otherwise specifically recited herein, the composition of thezincate solution and all conditions used in dissolving the cellulosefibers in zincate solution may be and preferably arethose described inthe said copending application orin my Patent No. 2,322,427 issuedJune22,1943, for Cellulose product, only the size of the fibers beingdifferent.

water. a

. I have now found that a great improvement is made when the cellulosewhich is used has been previously. finely comminuted, as. by cutting orotherwise forming the fibers into short lengths and exposing parts orthe fiber that were initially in the interior thereof. Such comminutedfibers dissolvereadily ineitherthezincate or hydroxide solutionunder theconditions stated, with the with the shorter lengths of fibers, there isnot only increased speed of solution in the alkali metal zincate orhydroxide solution, but also the final solutions of the short fibershave less tendency to'gel upon standing after the solution is Cut rayonyarn, for example, of mean fiber Qlength of approximately 200 microns,dissolves at a satisfactory speed to give a solution that does not gelover aconsiderable period after the solution is formed. Another rayonproduct out to a mean fiber length'less than 140 microns dissolves Whenthe alkali metal hydroxide solution-.is

used in place of the zincateand the sodiumhy-- droxide is tobedilutedsubsequent to contacting rapidly iii-zincate or hydroxide underthe conditions described above and gives a solution that -remains clear.for many days.

Wood pulp or other cellulose that has been cut to microns or less inmean length of fiber dissolves still more rapidly and gives asatisfactorily clear solution that does not gel within several weeks.

There is no lower limit to the fineness to which the cellulose may becut for use in accordance with the present invention. Any fiber, fromthe shortest length that it is practicable to manufacture, up to a meanfiber length not substantially above 200 microns is satisfactory. Theshorter lengths within this range are preferred. They dissolve fasterand give better stability of the finished solution.

Any convenient means of comminuting that is usual in finely subdividingmaterials similar to cellulose may be used as, for example. cutting,grinding, or shredding equipment. Thus, there may be used a fioccingmachine which is standard in the textile industry or a shearing machinefor velvets or the like set to cut the desired length of fiber from avelvet. Trimming from a rayon velvet may be used.

Although sodium hydroxide is ordinarily the alkali used in making thealkali metal hydroxide solution or with zinc oxide in making the alkalimetal zincate solution, potassium hydroxide may be substituted mol formol for the sodium hydroxide. Sodium hydroxide is preferred, however, asthe alkali to be used. Sodium zincate with excess of the hydroxide andsodium hydroxide dissolve the comminuted cellulose satisfactorily andthe sodium compounds are available or producible at a satisfactory cost.

As the source of cellulose there is used to advantage a cellulosicmaterial such as cotton, cotton linters, wood fibers, wood pulp of whichsulfite pulp is a good example, scrap rayon, or a cellulose ether ofwhich methyl, ethyl, and hydroxyethyl cellulose are examples of suitablematerial. These ethers are known to be alkali stable. Non-cellulosicmatter that may be present in the raw mation of water that the finalconcentration of sodium hydroxide is approximately 8 to 12 parts for 100parts of water and preferably is within the range of 8 to parts.

terial selected and that remains undissolved in my treatment may beseparated by filtration or sedimentation after the solution is made. Inany case it is required that the selected cellulose before contactingwith the solution to dissolvethe cellulose must be comminuted to fibersize described above.

In the preferred order of mixing, the comminuted cellulose is suspendedinitially in a part or all of the water to be used in making the finalsolution. To the slurry, there is then added the selected amount ofsodium hydroxide either in the form of a very concentrated solution orin dry form. When subsequent dilution is to be effected, the amount ofalkali added is that required to make the concentration of the sodiumhydroxide, after dissolving, equal to. or above the salting outconcentration. that is, the concentration adequate to causeprecipitation of cellulose previously dissolved, say, in sodium zincateor hydroxide, such a concentration being about 15 to 50 parts of thesodium hydroxide for 100 parts of water. Particularly satisfactoryresults are obtained when sodium hydroxide is added to establish theconcentration of its solution at this stage at about 16 to 30%.

The mixture of the strong sodium hydroxide solution and comminutedcellulose so made is allowed to stand for a sufficient time for thesolution to penetrate the cellulose thoroughly. Then there is introducedwater in such amount as to inake the final concentration of the sodiumhydroxide solution less than that which salts out the cellulose (as froma previously prepared solution) but at least equal to the minimumconcentration required to retain in solution cellulose that has beendissolved in sodium hydroxide. Thus, the dilution is made with such apropor- While the dilution may be made and the added water stirred inuniformly in any convenient the water in small portions or continuouslywhile the whole mixture is being stirredr In another embodiment, thedilution of the relatively concentrated zincate or sodium hydroxidesolution first used is eflected by means of melting ice, so that the iceserves to supply water at a more or less regular rate as the ice melts.In this case the amount of ice used is such that, when all is melted orwhen the unmelted portion of the ice is separated by draining oil theliquid while holding back the ice, the sodium hydroxide will have .beendiluted to the final concentration within the range recited above.

Solutions of the comminuted fibers in zincate are made to advantage asdescribed in my said patent and copending application, the comminutedcellulose being substituted pound for pound for the cellulose describedin the said patent and application. I

Particularly rapid rates of solution are obtained when cellulose is notonly comminuted but also of reduced viscosity. Thus, there is used toadvantage cellulose fiber of the kind described that has been reducedsubstantially in viscosity, say to about three-fourths to one-tenth orsomewhat less of the original, as by any conventional viscosity loweringtreatment.

The finely divided fibers when treated as described above dispersequickly in the solution of sodium zincate or hydroxide, the treatmentfollowed by dilution giving satisfactory results even at ordinarytemperatures. The solution occurs so rapidly that there is nosubstantial difliculty of objectionably long contact with the sodiumzincate or hydroxide such as, if required along with low temperatures toeffect solution in the first place, would cause gelatinization ofcellulose first dissolved before the last of the cellulose is dissolved.

After all the cellulose or cellulose derivative used is dissolved, asshown by the formation of a clear or nearly clear liquid mass, thesolution is warmed promptly to about 15 to 25 C. (unless already thatwarm), so as to stabilize the solution and minimize subsequent gelation.

With cellulose fibers that have been cut to length stated above and thentreated to reduce the viscosity by at least a third or more, sodiumhydroxide gives solution in about 10 to 20 minutes or less, when thehydroxide at high concentration is contacted with the fibers and issubsequently diluted as described. Zincate solutions are formed in anequal or shorter period.

The invention will be further illustrated by description in connectionwith the following specific examples.

Example 1 A low viscosity'cellulose is made by cutting wood pulp in afioccing machine, tofibers of mean length 137 microns, and heating thecomminuted wood pulp for 12 hours at C. Ten parts of this cellulose aretreated with 20 parts of 40% sodium hydroxide solution. This treatmentis accomplished by soaking the cellulose in a large volume of. thecaustic at room temperature, such as 10' to 30 (2., and then pressing sothat each pound of cellulose retains Zparts of the hydroxide solutionThis pressed material is shredded and kneaded for one hour and then '70parts of water, also at about room temperature or'about 10 to 30 0.,areadded to make approximately 100 pounds of solution. This results in aclear cellulose solution. I

" Example 2 Example 3 Sulfite wood pulp is ground in any usual manner,as by ball milling a slurry of the pulp in water, until the ground pulpcan be slurried with four parts of water to one of the pulp.

The comminuted pulp is then treated with about 5 to 10 times its weightof a 0.05% solution of hydrogen peroxide in water in an iron vessel, ata temperature of 95 to 100 C., for an hour or so. to lower the viscosityto approximately a sixth of the original viscosity of the cellulose, theviscosity being measured by dissolving samples of the untreated andtreated cellulose in cuprammonium solution and determining the relativefluidities of the two solutions.

This short fiber cellulose of reduced viscosity is made into a slurry inthe proportion of 10 parts of the cellulose to 100 parts of water. Tothis slurry there is then added 25 parts of commercial flake sodiumhydroxide. The whole is stirred as the sodium hydroxide is being addedand for some time thereafter, so as to make certain that there isthorough contact of the cellulos with the uniformly concentratedsolution of sodium hydroxide and that the solution penetrates thecellulose.

After about 15 .minutes contact of the hydroxide solution with thefibers, there are introduced 150 parts of cracked ice. The whole is thenstirred, the ice melting gradually and serving to dilute and cool themixture.

This example may be varied, as in the amount of ice used. Thus, theamount of ice used may be so selected-as to cause the temperature of themixture after melting of the ice to be between and 15 0., say about 2 to-8 0. Such low temperatures are favorable to the rapid solution of thecellulose that has been contacted with the concentrated sodium hydroxidesolution, upon dilution of the latter, but such temperatures are notrequired for a satisfactory rate of making such solution.

7 Example 4 Example The procedure of. any of the above examples isfollowed except that there is substituted cut rayon or Cellophane wasteor one of the cellulose ethers referred to above, the substitution beingmade on the basis of 1 part of the substituted material for 1 part ofthe cellulose.

stantially free from zincate.

Example 6 The procedure of Examples 1 to 5 is followed except that thereis substituted, for the sodium hydroxide solution used initially, asolution made from 18 parts .of sodium hydroxide, 6 parts of zinc oxideand 76 parts of water. Suitably the zincate solution is used in theproportion -of 6 to 10 pounds for 1 pound of the comminuted cellulose,the cellulose is pre-slurried with water, and the whole mixture aftercontact of the zincate solution with the cellulose is diluted asdescribed to a final concentration of titratable.

alkalinity calculated as sodium about 8 to 12per cent.

To stabiliz the solutions made in accordance hydroxide. of

with any of the above examples, the solutions are preferably warmedpromptly after being made, to a temperature of about 15 to 50 0.provided the solutions have been made initially at lower temperatures.

Solutions made as described herein are practically clear.

The cellulose present is precipitated by various precipitating agents asby the addition of sul-- It will be understood also' that it is intended.to cover all changes and modifications of the examples of the inventionherein chosen for the purpose of illustration which do not constitutedepartures from thespirit and scope of the invention.

What I claim is:

1. In making a solution of cellulose, the method which comprisestreating cellulose of mean fiber length not substantially above 200microns with a solution of an alkalimetal hydroxide containing dissolvedalkali metal zincate.

2. In making a solution of a cellulosic material, the method whichcomprises treating a cellulosic material consisting essentially ofmaterial selected from the group consisting of cellulose and alkalistable cellulose ethers and having a mean fiber length not substantiallyabove 200 microns with a solution of an alkali metal hydroxide at aconcentration at least equal to the salting out concentration fordissolved cellulose and then diluting the sodium hydroxide to aconcentration not substantially above 12 per cent. a

3. In making a solution of a cellulosic material, the method whichcomprises treating a. cellulosic material consisting essentially ofmaterial selected from the ,group consisting of cellulose and alkalistable cellulose ethers and having a mean fiber length not substantiallyabove 200 microns with a solution of an alkali metal hydroxide at aconcentration at least equal to the salting out concentration fordissolved cellulose and then cooling and diluting the sodium hydroxideto a. concentration notsubstantially above 12 percent, at-a temperaturebelow 5C. but above the freezing point of} any inorganic materialpresent, the alkali metal hydroxide solution used being sub- 4. Themethod described in claim 1, the cellulosic material being cellulose,the mean fiber length being less than 140 microns, and the alkali metalhydroxide solution used being substantially free from zincate.

5. In making a solution of cellulose the method which comprises treatingcellulose 01 mean fiber 5 summons crrm The following references are ofrecord in the Number Number 15 403 783 file of this patent:

UNITED s'rxrns PATENTS Name Date Swinehart et a1. Oct. 12, 1943 Richter.May 29, 1934 Richter Jan. 5, 1932 Edelstcln 1 June 22, 1943 FOREIGNPATENTS 'Gomtry Date German' 0ct.v4, 1924

